Light responsive system



y 1952 G. w. ONKSEN, JR

LIGHT RESFONSIVE SYSTEM Original Filed July 10, 1948 2 SHEETS-SHEET lIhwentor @aga @2%W/m/z May 27, 1952 G. W. ONKSEN, JR

LIGHT RESFONSIVE SYSTEM Original Filed July 10, 1948 2 SHEETSSHEET 2Patented May 27, 1952 2,598,420 LIGnr ltnsr'onsivn SYSTEM GeorgeQnksenrjn, Anderson, Indl, assignor to General MotorsCorporation,Detroit, Micli., a ccrpofation of Delaware Giigin'al application July 1I948, Serial No; 37,984: Divided and this application June 30, 1950,Serial No; 171,363

55 Claims.

No. i198}; filed July 16, N48,; in the. names of George W. Onkserr, Jr.,and- Charles W. Miller,

entitled-f1 flight Responsive System!" Inc illumination systems ofautomotive ve-.

hiclesare generally provided with dual filament headlamps witheachfilament in separate l y energiza-bleelectrical circuits controlledfor alternate energization by the operator. i The filament arepositioned with respect to the headlamp reflector to project a high andvlow beam of light declining to thelongi-tudinal axis of the vehicle atdifferent angles so that illumination patterns are cast atdi-iferentdistances inits path ahead. The high beam is generallypreferred for nightdriving on rural highways which are not illuminatedfromother sources, whereas thelow beam is generally used for citydriving conditionswhere additional illumination is provided: i

To eliminate theha zard-s of passing due to the glare and dazzling qeffect of the high beam; the operator is required to manually; operate aswitch which selectively energizes the low beam circuit. Thisoperationma-y distract the operators attentionfrom; the path ahead andwhen the operator tailsto depress the beam, extremelyhazardousconditions prevail for the passing of oncoming era rs It is therefore anobject of the present invention to minimize the driving hazardsprevalent under conditions of night driving by providing alight-sensitive electrical circuit for automatically controlling theillumination system of vehicl'es in response to the intensity ofillumination of a similar approaching system.

This and other objects are obtained in accordance with the presentinvention by providing a selective light-sensitive electrical circuitfor con; trolling vehicle headlighting' systems which is responsive to apredetermined light intensity to dim the systemyet may be subjected to'awide variation of light intensity without affecting a d-enrgization ofthe dim circuit once it has been energized. A headlight system embodyingthe present invention comprises the conventional dual filament headlampswith independent electrical circuits for energizing one or the other alight-sensitive electrical circuit including aphotoelectriccell, a firstand second stage of amplificationya relay" for selectively energizingthe inde- 2 pendent filament circuits and a common source of electricalenergy. The responsiveness to a predetermined light-intensity whileremaining un affectd by Wid variations of light intensities once thesystem has been dimmed is obtained by including in the second stage ofamplification,

tow amplifier tubes of difiring characteristics electrically connectedin parallel.

Further objects and advantages of my invention will become apparent asthe renewing description proceeds and the features of novelty whichcharacterize my invention will be pointed outwith particularity in theclaims annexed to and forming part of this specification.

For better understanding of my" invention reference may be had to theaccompanying drawings in which Figure 1 is a schematic diagram of thecircuit utilizing the present invention for controlling a vehicle.headlightin'g system; Figure 2 is a schematic diagram illustrating oneform of modif cation and Figure 3 is a schematic diagram illustratingstill another modification.

Referring now to Figure l of the drawings, there is illustrated avehicle headlighting system embodying the present invention in whichapair of conventional headlamps, not shown,

including high and low beam filaments 2' and 4 respectively,- form partof electrical circuits energizable to provide either a manual or'automatic control of the system.

In the system,- a conventional automotive vehicle storage battery 6 ofthe 6-volt type is provided as a source of electrical power. In thisconnection it will be understood that the battery 6 is a source of powerfor the ignition system of the vehicle as well as the lighting system.The negative terminal of battery} is connectedto ground and thepositiveterminal is connected through conductor 8 to the movable arm IDof asingle pole,-. sing-1e throw master switch l2." The stationarycontact [4 of Switch; E2 is connected through conductcr l6, currentlimiting fuse l8 and conductor 20 toa terminal junction 22'. A branchconductor 24; connects terminal 22 with the movable arm 28 of a singlepole, double throw electromagnetic relay switch 28 provided withoppositely disposed. stationary contact terminals 30" and 32. Themovablearm 26' of switch 28 is normally held in yieldingengag e rnent withstationary contact terminal 32 which in turn is connected throughconductor 34 to the low beam filaments Qof theheadlan psl The other sids(if the headlamp filaments 4 are grounded uirdugn" a-condu'ctor 36. Thecircuit comprising contact 32, conductor 34, filaments 4 and conductor36 form one branch of the headlamp circuit. The other branch comprises aconductor 38 which connects the high beam filaments 2 of the headlampsto contact 38 of the switch 28 and conductor 48 which connects the othersides of the filaments 2 to ground.

To provide for the independent manual energization and deenergization ofthe headlamp circuits, the solenoid coil 42 of switch 28 forms part of acircuit which includes in series relationship a single pole, doublethrow, selector switch 44 and a single pole, double throw foot selectorswitch 46. Terminal 22 is connected to the movable arm 48 of switch 44through conductor 58. The movable arm 48 is shown in a position tobridge two stationary contacts 52 and 54, both of which are connected incircuits to the automatic control and indicating means and will bedescribed in detail hereinafter. An oppositely disposed contact 56 ofswitch 44 is connected through conductor 58, terminal 68, conductor 62,terminal 64 and conductor 66 to a stationary contact 68 of the footselector switch 46. The movable arm I8 of switch 46 is adapted to engagecontact 68 and complete a circuit through conductor I2, solenoid coil 42of switch 28 and conductor I4 to ground.

For automatic control of the headlamp filaments a circuit is providedfrom the source 6 to the solenoid coil 42 which includes alightresponsive, single pole, single throw electromagnetic relay switchI6 capable of energization and deenergization at substantially differentcurrent values. In this circuit the stationary contact 52 of selectorswitch 44 is connected by a conductor I8 to a terminal junction 88 whichin turn is connected to the movable arm 82 of relay switch I6 throughconductor 84, terminal junction 86 and conductor 88. The movable arm 82cooperates with stationary contact 98 of relay switch I6 and is normallyin yielding open circuit relationship. Contact 98 is connected throughconductor 92, terminal junction 94 and conductor 96 to the remainingoppositely disposed stationary contact 98 of foot selector switch 46.,

To reduce the destructive efiect of arcing between the movable arm 82and the stationary contact 98 of relay switch I6, a shunt circuitincluding a 100 ohm resistor 100 and a .1 mfd. capacitor I82 isconnectedin series between the terminals 86 and 94.

In the headlighting system of the present invention the voltagessuitable to the most eificient operation of the light responsiveapparatus are provided by a conversion device I84 for changing the lowvoltage direct current of the vehicle electrical system to'a highvoltage direct current suitable for the operation of the electronicelements in the circuit. Conversion devices such'as the device employedin the system of the present invention are well-known and are employedextensively to provide suitable voltages for the operation of vehicleradios. In this connection the positive input terminal I86 of theconverter is connected through conductor I88. terminal junction H8 andconductor II2 to the terminal 88. The negative terminal I I4 isconnected to ground by conductor III. The high voltage output terminalH6 is connected by a conductor II8, terminal junction I28, conductorI22, terminal junction I24 and conductor I26 to the solenoid coil I28 ofthe light responsive relay switch I6. The

negative output terminal of the converter is connected within theconverter to ground through terminal H4. The light responsive relay I6has the other end of its solenoid coil I28 connected through conductorI38, terminal junction I32, conductor I34, terminal junction I36, a25,000 ohm resistor I38 and conductor I48 to the stationary contact I42of a single pole, single throw, manual switch I44. The movable arm I45of switch I44 is in yielding open circuit relation with contact I42 andis connected to ground by conductor I46. A shunt circuit is provided forthe solenoid coil I28 of relay switch I6 which includes an 8 mid.capacitor I43 connected between the ends of the solenoid coil.

To provide the different voltages necessary to the operation of thevarious electronic elements in the light responsive apparatus a voltagedivider network I4'I comprising 4 sections of series-connectedresistances I48, I58, I52 and I54 of 5888 ohms, 880 ohms and 15,000 ohmsrespectively, is connected between the high voltage terminal I24 andground. The respective resistances are connected together in the orderenumerated by terminals I56, I58 and I68.

A filter I62 or 16 mfd. capacitance is connected across the outputterminals II 6 and II 4 by means of conductor II8, terminal I28,conductor I68 and conductors I I8 and I I I, to minimize the A. C.ripple voltage that is present in the output circuit of the converter I84.

As the voltage at the output terminals of the converter varies betweenabout 260 and 420 volts due to the variation of the vehicle systemvoltage between about 5.5 and 7 volts, voltage regulator means I64 andI66 are connected in parallel with sections of the voltage dividernetwork M1 to obtain stable voltage levels of 150 and voltsrespectively. The voltage regulator means I64 and I66 comprise a VRl50glow discharge tube which is connected by conductors I12 and H4 betweenterminal I56 and ground, and a VR75 glow discharge tube which isconnected by conductors I 16 and H8 between terminal I68 and ground.

The electronic elements that comprise the light responsive apparatus andprovide for the energization and deenergization of relay switch I6include a photocell II9 which controls a power amplifying tube I98hereinafter referred to as a first stage or primary amplifier and a pairof power amplifying tubes I98 and 286 which are controlled by the outputof the primary amplifier and have their plates connected in parallel tothe solenoid coil I28 of the relay switch I6. The pair of amplifyingtubes I98 and 286 will be referred to hereinafter as the second stage orsecondary amplifier. The photocell I19 is connected to the voltagedivider M1 by a conductor I88 which connects its anode terminal toterminal I58 at the junction of the voltage divider resistance sectionsI58 and I52. By connecting the photocell anode to the voltage divider atthis point, a voltage of about to volts is provided for the operation ofthe cell at the most efficient portion of its response curve. Thecathode of the photocell is connected by conductor I8I to a terminaljunction I82 which in turn is connected through a 500 megohm resistorI84 to ground and to the positive terminal of a one and one-fourth voltbiasingbattery I86 which has its negative terminal connected by aconductor I88 to the control grid of the multiple grid power amplifyingtube I88 comprising the first stage or primary amplifier. The output orplate of tube I98 is connected by conductor I 92, terminal junction I94and conductor I96 to the-control grid-of themuh tiplegrid poweramplifying tube" I 66 comprising partof the second stage or secondaryamplifier and through terminal I94, resistor I96, terminal junction I91,conductor 200, resistor 202'- andconductor 204 tothe control grid of themultiple grid power amplifying tube 266 comprising the other part ofthe-second-stageorsecondary amplifier. The resistors I65 and 202 haverespectiveresistance values of 2 and 100 megohms. The plate of tube I95)is also-connected-by terminal- I91 to terminal 5-58 of the voltagedivider through an 8 megohm resistor 208, conductor 2 I 0, terminaljunction 2I2 and conductor 2I-4. A- 70,0'00 ohm potentiometer 2I3 isconnected between termi-nal 2I-2 and ground and carries a slidingcontact 2I 5'which is connected by a con-- ductor 216 to the screen gridof first stage amplifying tube I00. Current for heating the filament oftube- I66 is supplied by connecting the filaments of tubes I90 and I98are connected to ground. To obtain a stable voltage input of 156 Currentis also supplied volts to the screen grids of tubes I98 and 206 of forthe cathodes of tubes I68 and 266 are-supplied fromthe' voltage dividerI41; the cathode and suppressor'grid of tube I98'being connectedby'conductor 232m terminal 2I2' and the cathode and i suppressorgrid oftube 266' being connected by conductor234 to the sliding contact 236 onthep'otentiometer section I54. The cathode of tube 206 is heatedby anindependent filament which has one side connected: by conductor 235' tothe 6-volt' battery source at the junction of conductor" 88 and movablearm 82 of switch 16 and the other side" connected to ground. The platesof the tubes I98'an'd 206' are connected in parallel to the solenoidcoil I28 ofrelay switch 16", the plate of tube 206* being connected toterminal I32 through a j-000 ohm' resistor I33 and the plate oftu-be I96being" connected to terminal I36 by conductor'23B.

Indicating means for the'li'ght responsive and manual control circuitsare included in the switchingcircuit': These means comprise indicat'orlamps 250' and 242. Lamp 240 has on'e'si'de of its filament connectedto" terminal 60 byconductor 24-4 and the other side of the filamentconnected' to the contact 54 of switch 44 by conductor 246, junctionterminal 248 and conductor 260. The filament of lamp 242 has one sideconnected to ground and the other side connected through aconductor 252to'the stationary contact 254= ofan electromagnetic relay switch 256.The movable arm 255 of the relay switch 256 is in" yielding closed'circuit relationship withcontact 254" and is connected by'conductor'251;.te'rminaljunction 259 and conductor 26I' to the'terminal 2481 Thecoil 263 of the relay 256 is energized through a circuit whichco'mie'cts one: end of the coil through a conductor 265 to terminalB4'andthe other end of coil to. terminal 256.

In the circuit modification of the light responsive apparatusillustrated in Figure 2, the air connection with the circuitofl igure I.

. 206 by conductor 26-1.

rangement of a the circuit and electronic elements"- is substantiallythe-same as that of Figure 1:exce'ptthat a duc diode tube 256" iscormected between' the'multi pl'e grid tube I90 or theprimary amplifierand: the multiple grid tube 206- oi the secondary amplifier.-

In this circuit the plate of: the primary am pl ifier tube I90 isccnnecte'd to terminal I94 by conductor" I92 withbranch circuitsconnecting: terminal I94 with thecontrol grid of tube I98 one ofthecathodesof tube 256 and the volt terminal or the voltage divider In.-The circuit connecting the grid oftube I98 and'thc plate oftube is thesame as hereinabove described in: Tliecir cult to the 75 volt" terminalof the voltage divider includesa lo megohm' resistor 260 connectedlieftween terminals H14 and 2l2 byconductors zia and 262.- -A conductor255 connects terminal 94 with the cathode of tube 256: The voltage ofthe control and oftube 206 controlled 'by" the output plates crtube fisxThese plates are cohf nected in parallel circuits to" aterminal'junction 265: which is connected tothe-contrcl-g' rid of tube oneplateor the diode-is connected to terminal 265- through a 1 volt biasingbattery 268 which has its positive terminal connected totheplate'of'tube2-56' by con-- ductor'2-69 and itsnegative-terminal-connected to terminal 265' by conductor 266.Theotherplate ofitube2'56' is connectedto' terminal' 265 by-co'nduct'or' 264. The heater fil'ame'nts' of tube 256' are'connected inseries between ground and the conductor-235 by conductor- 21I-.- Ther'emaining cathode oftube 256' is connected through a 2 megohm' resistor213- to the cathode of tube 206.

In the circuit modification of the light responsive apparatusillustrated in Figure 3- there is in cluded apair'ofmultiple grid tubes210 and 212'- comprising a first stage or primary amplifier whichhave'their outputs controlled by the photo-- cell and which inturncontrolthe outputs of another pair of multiple grid tubes 214- and216' comprising a second stag'eor secondary amplifier;-

In this circuit arrangement the control-grid oftube 212 isconnectedtothe' cathode of the-photo cell I19 through conductor 218,terminal unction 280 and a 1% volt biasing battery 282' which isarranged with its negativeterminal connected-to th'e control grid andthe-positive terminal connected to the terminal 280. A- meg'ohmresistor' .284: in series witha 500 megohm -resistor 286' are connectedbetween terminal 280 and ground. A conductor 288- connects thejunctionof resistors 284 and 286'to the control grid of tube 210. Theplates of tubes 210 and 212 are con-- nected' respectively by conductors290 and 29-2- to the control grids of tubes 214 and 216. Currentis-sup'plied to-the filaments of tubes 2-10, 212' and 216 from the6-volt battery circuitthrough tar-- minal IIII, choke coil 2I8andballast r'esistor'220 and-the branch circuits'c'omprising the condu'ctors 294- and 296-. The filaments of tubes 210 and 212 are connected inseries circuit relationship between conductor 294 and ground byconductors 298 and 300 while the filament of tube 216- hasone sideconnected to groundby conductor 302 and the-other side connected to-theconductor: 296. Voltage is supplied to the screen grid oftube 212 by acircuit which connects one end-of a 70,000ohm potentiometer 304- to the75 volt terminal I60 of the voltage divider I41 and theother endof theresistor to ground. Resistor-304 is connected to terminal I60 by acircuit which includes conductor 2T4, junction terminal 308,conducto'r'flll; junction terminal 3I'2, conductor 3I4, junctionterminal 3 I6 and conductor 3I8. A slidable contact 320 associated withthe potentiometer 304 is connected by a conductor 322 to the screen gridof tube 212. Voltage is supplied to the screen grid of tube 210 byconnecting the grid through conductor 324 to a slidable contact 236which is associated with the potentiometer section I54 of the voltagedivider I41. The cathodes and suppressor grids of tubes 214 and 216 areconnected respectively to terminals 308 and 3I6 by conductors 328 and330; the suppressor grid of tube 214 being connected to the cathodeexternally by conductor 321. A 250,000 ohm resistor 332 and a 500,000ohm resistor 334 are connected respectively between the plate of tube210 and terminal 3I2 and the plate of tube 212 and terminal 3 I 6.Current is supplied to the filament of tube 214 by conductor 235 whichis connected between the movable arm 82 of relay switch 16 and one sideof the filament.

The other side of the filament of tube 214 is connected to ground byconductor 338. The plates of tubes 214 and 216 are connectedrespectively to terminals I32 and I36 in the coil circuit of relayswitch 16 through a 100,000 ohm resistor 340 and conductor 342.

For the hereinabove described light responsive circuits to operate inresponse to predetermined light intensities to control the energizationand deenergization of the headlamp filaments 2 and 4 through relayswitch 16 it is first desirable to adjust the circuit to respond withpredetermined current flow at the plate output of the tubes of thesecondary amplifier. In this connection, switches I2 and 44 are closedto energize the current converter I04. The electronic elements which areconnected to the high potential side of the converter are allowed toheat for a period of time'so that they will operate efliciently. Thesliding contacts of the three circuits are then adjusted to providecurrent flow through coil I28 which will vary in accordance with theintensity of light of an approaching vehicle headlight system to causedeenergization of the coil when the approaching vehicle is at apredetermined distance ahead and energization of the coil when theapproaching vehicle passes by.

To provide for the automatic control of the headlighting system, switchI is closed to energize the low beam filaments 4 through current flowfrom the battery 6 through conductors 8, I6, I8, and 24, movable arm 26and conductor 34. The movable arm 48 of switch 44 is then closed oncontact 52 to energize the converter I04 through the circuit includingconductors 18, H2 and I08.

Referring now to the circuit diagram of Figure 1 with the electronicelements sufficiently heated and no light on the photocell I19,sunicient current flows in the circuit from terminal II6 of theconverter through conductors II8, I22, I26, coil I28, conductors I andI34 to the plates of tubes I98 and 206 to cause energization of therelay coil I28 and movement of arm 82 of relay switch 16 into engagementwith contact 90. With the movable arm 10 of the foot switch 46 engagingcontact 98 a circuit iscompleted to coil 42 from the battery throughconductors 8, I6, 20, 18, 84, 86, 62, 96 and 12. With coil 42 energizedthe movable arm 26 of relay switch 28 moves into engagement with contact30 causing energization of the high beam filaments 2.

With the approach of a similar lighting system, light of graduallyincreasing intensity falls on the photocell I19 causing an increasingcurrent flow from terminal I58 of the voltage divider through conductorI80, photocell I19, conductor I8I and resistor I84 to ground. With thegradually increasing current flow in this circuit the voltage atterminal I82 changes and gradually overcomes the negative grid bias onthe control grid of tube I caused by the biasing battery I86. As thebias on the control grid gradually changes from negative toward positivethe flow of current from terminal I60 of the voltage divider throughconductors 2 I4, 2 I0, resistors 208 and I and conductor I92 to theplate of tube I90 increases and a voltage drop occurs at terminals I91and I94 due to the IR. drop across resistors I95 and 208. These voltagechanges are carried to the control grids of tubes 206 and I98respectively through circuits including conductor 200, resistor 202 andconductor 204 and conductor I96 respectively. This causes a change ofgrid bias on the control tubes I98 and 206 causing both tubes to becomesequentially non-conducting; the tube I98 being the first to out off,but relay I28 will not drop out until tube 206 is cut down inconductance to a low value after tube I98 is nonconducting. With verylittle or no current flowing to the plates of tubes 206 and I98 the coilI28 of relay 16 is deenergized moving arm 82 out of engagement withcontact 90 and the circuit through coil 42 of relay 28 is broken causingthe movable arm 26 to move into engagement with contact 32 for theenergization of low beam filaments 4 and the deenergization of high beamfilaments 2.

If the source of illumination to which the photocell is exposed thenbegins to decrease in intensity, a current of decreasing value flowsfrom the terminal I58 of the voltage divider through the circuitincluding the photocell to ground as hereinabove mentioned. Accordingly,the voltage at terminal I82 decreases until the voltage of the biasingbattery is imposed on the control grid of tube I90. The flow of currentthrough tube I90 decreases and consequently the voltages at terminalsI91 and I94 increase altering the grid bias in tubes 206 and I88. Asthese biasing voltages change the flow of current in tube 206 graduallyincreases to normal value, and tube I98 begins to approach theconducting point. However, While tube I98 remains non-conductive thereis insufficient current flow in the coil circuit of relay 16 to cause itto move the arm 82 into engagement with contact 90. When it does becomeconductive sufficient current flows in the relay circuit to cause relay16 to move the arm 82 into engagement with contact 90 and filaments 2and 4 of the headlamp circuit respectively are energized anddeenergized. There is thus a definite difference in the illuminationlevel at relay drop-out to that at relay return. With this arrrangementit will be obvious that substantial changes in intensity of illuminationare required before the relay 16 will be energized or deenergized fromits existing state thereby preventing flickering or repeated alternateenergization of the filaments due to extraneous lighting conditions.

If the operator of the vehicle should desire to reenergize the high beamelements 2 while the low beam elements are energized and under thecontrol of the light-responsive apparatus. the independent resettingmanual foot switch I44 is provided to close a circuit through the coilI28 of relay 16 from the terminal I I6 of the converter I04 to ground.This circuit comprises conductors II8, I22, I26, relay coil I28,conductors I30, I34,

resistor I38, conductor I40, switch 144 and conheadlight system. .Inthis connection the movable arm 48 of selector switch 44 is moved intoengagement with contact .56 thereby completing a circuit from battery .6through conductors 8, I6.,.20, 58,58, .62 and 66 to the stationarycontact 68 ofrthefoot switch '46. Whenthe movable arm 18 moves intoengagement'with contact 618, the circuit is completed from the battery 6to the coil of relay ,28.through the switch 46 and conductor 12. Movablearm 26 of relay switch 28 moves into engagement with contact 38 and thehigh beam filaments 2 are energized. Manually breaking the circuit atswitch 46 causes a deenergization of relay coil 42 and an energizationof the circuit to the low beam filaments 4.

Lamps 240 and 242 indicate the controlling condition of the lightresponsive apparatus and the respective energization of the headlampfilaments. With the movable arm 48 of switch 44 in engagement withcontacts 52 and 54 for energization of the light responsive apparatusare hereinabove described, a circuit is completed from terminal 248through conductor 246, lamp 246 and conductor 244 to terminal 68. Anadditional circuit is completed from terminal 248 through conductor 26I,coil 263 of relay switch 256 and conductor 265 to terminal 64. Thiscircuit also includes a branch circuit from conductor 26I to the movablearm 255 through conductor 251. With the coil of relay switch 256deenergized, this circuit is completed through contact 254, conductor252 and lamp 242 to ground. When the arm 18 of switch 46 is inengagement with contact 98 for control of the filaments 2 and 4 by thelight responsive apparatus, lamp 242 is energized, indicating that thelight responsive apparatus is controlling. When the movable arm I8 ofswitch 46 moves into engagement with contact 68, coil 263 of relay 256is energized moving arm 255 out of engagement with contact 254 wherebythe lamp 242 is deenergized. At the same time, lamp 240 becomesenergized. With switch arm 48 moved out of engagement with contact 54both indicating lamps become deenergized. With such an arrangement ofindicating lamps there is visual means for indicating which of theheadlamp filaments is energized when they are controlled manually andwhether the filaments are under the control of the light responsiveapparatus.

The operation of the light responsive circuit of Figure 2 issubstantially the same as that of Figure 1. In this circuit, theintensity of light on the photocell determines the current flow in tubeI96 and through resistor 266 which in turn controls the current flow intubes I98 and 286 by changing the voltage on the control grids of thesetubes. With no light on the photocell, both tubes I98 and 266 conductsufficient current to cause the energization of coil I28 of relay 16 ata substantially high current value. As the photocell becomes exposed toincreasing intensities of light, the voltage bias on the control gridsof tubes I98 and 286 causes the tube I85 to become non-conductive andreduces the current fiow of tube 286 to a sufficiently low current flowto cause relay coil I28 to become deenergized. Current value at whichthe relay coil becomes deenergized is substantially less than that atwhich it becomes;

energized. In this circuit the purpose of the diode tube 256 is toreplace resistor 262 of the circuit arein turnicontrolled by thephotocell.

of .Figurel and 'preventthe control grid of tube 286 from becomingpositive with respect to the cathode.

Inthe lightresponsive circuit of Figure .3 the operation issubstantially the same as that of light responsive circuits of Figures 1-and'2 except that'the flow of current through tubes 214 and 216 isdirectly and separately controlled by tubes .216 and 212 respectively ofthe primary amplifier. Thesetubes of the primary amplifier As in the.light responsive circuits of Figures 1 and 2 Whenthe photocell is notexposed to light tubes 214 and 21.6 :both conduct current ofsubstantially high valueto energize relay coil I28. As the'intensity oflight on the photocell increases the photocell conducts increasinglymore current in the circuit from the voltage divider to ground throughthe photocell, conductor 218 and resistors 284 and 286. With increasingcurrent in this circuit voltage changes occur across resistors 284 and286 to cause the voltage bias on the control grids of tubes 210 and 212to change, thus changing the current output of the tubes 214 and 216 andthe voltage bias on the control grids of tubes 214 and 216. Withsufficient light intensity on the photocell, tube 216 no longer conductscurrent and tube 214 conducts current of less value than that requiredto retain relay coil I28 energized. While specific circuit constantshave been used in connection with the description of the circuits of thepresent invention and their operation it will be understood by thoseskilled in the art that they are illustrative and that the circuits arecapable of operation at other values than those recited.

With the light responsive circuits such as described above wherein thelight responsive relay controlling the headlamp filament circuit is inturn controlled by an amplifier comprising two amplifier tubes inparallel, the energizing and deenergizing of the headlamp filaments isaccomplished at substantially different intensities of illumination.This important feature makes the operation of an automatic dimmer devicefor vehicle headlighting systems feasible because of the lack ofresponse of the device to other sources of light causing flickering dueto the repeated energization and deenergization of the high and low beamheadlamp filaments.

What I claim as new and desire to obtain by Letters Patent of the UnitedStates is:

1. In an automatic vehicle headlight control system, the combination ofpower supply, a phototube connected thereto, a dark actuated amplifiercircuit connected between the phototube and the power supply, a relay inthe output circuit of the amplifier, and an electronic means to pull onthe relay armature in the absence of light on the phototube, wherein,said relay armature operating as a means to automatically switch lightsfrom high beam to low beam upon the application of light and returningthem to high beam when the light is removed.

2. In a control for automatically dimming multiple filament headlamps, alight sensitive pick-up device, a source of electrical power, voltageamplifier means connected to the source of power and to the pickupdevice, current amplifying means connected to the output of the voltageamplifying means, a relay connected to the output of the currentamplifying means, said relay being normally energized in the absence oflight on the pickup device and deenergized upon the application of lightthereto, and a switch operated by the relay to change the power sourcefrom the headlight high beam to the headlight low beam filament when therelay is deenergized by light falling on the pickup device and uponremoval of the light to change the power source back to high beamfilament.

3. 'In a control system for automatically dimming multiple filamentheadlamps, a light sensitive pickup device, a source of electricalpower, a multi-element voltage amplifier tube connected to said sourceof power and having a control grid and plate, said control grid beingconnected to the pickup device, a current amplifier tube having acontrol grid and plate, said control grid being connected to the plateof the voltage amplifier tube and relay means connected in the platecircuit of the current amplifying means normally energized in theabsence of light on said pickup device and deenergized upon theapplication of light to the pickup device, and switching means operatedby the relay to change the power source from the headlight high beamfilament to the low beam filament when it is deenergized by lightfalling on the pickup device and return it to the high beam filamentwhen the light is removed.

GEORGE W. ONKSEN, JR.

No references cited.

